Think about this. An elite QB in college is 160+ An average one is 140 and a horrible one is 120 or less.

So set the scale at 120-160. Anything under 120 and you are the worst of the worst. Anything over 160 and you are elite. But to fit in that segment, which 80%+ of today's QBs do, you move up or down significantly depending on where you are.

Take the NFL. Lamar is currently an outlier (like 160+) and Jared Goff is 2nd with a PER rating of 110. Gardner Minshew isn't at the bottom (he is 28th out of 34) but is at 81% which is close to the line of putrid. Using your method of calculations that is an 18% difference. But Detroit averages 32.8 ppg and Las Vegas averages 17.5 ppg.

Would you say Goff and Minshew have played just 18% apart from each other this year. No. Rating isn't designed to calculate that way.